A major goal of this laboratory is the study of the biology and host responses to Giardia lamblia and cryptospordium. Both of these parasites are prevalent and cause disease in homosexuals and AIDS patients but also cause significant morbidity in the general population. Although Giardia is the most common disease causing intestinal parasite in AIDS and homosexuals, it is more readily treatable with conventional drugs than Cryptosporidiosis, which is not treatable wilth currently available drugs and therefore can be a serious and lethal infection in AIDS patients. Research on cryptosporidum has only recently begun. Several isolates have been obtained and are now maintained in vivo in suckling mice. There is preliminary evidence of differences in susceptibility to genetically deficient mice. One of the major problems has been getting enough parasite to raise antibodies, monoclonals and develop test systems. Recently, a number of calves were infected with this parasite and this has enabled us to obtain large quantities of infected stools which will, after purification of cysts, yield workable quantities of parasite.